Effect of a linear monomer on the thermomechanical properties of epoxy shape-memory polymer

The effect of a linear monomer on thermomechanical properties and shape recovery behavior of an epoxy shape-memory polymer is studied. These shape-memory polymers are prepared from epoxy base resin, hardener and linear epoxy monomer. As the content of the linear monomer increases, the glass transition temperature (T-g) determined using differential scanning calorimetry ranges from 37 to 96 degrees C. A decrease in rubber modulus is seen from dynamic mechanical analysis for the polymers, which reveals decreasing crosslink density with increasing linear monomer content. Tensile test results show that the elongation at break and strength depends on the content of linear monomer at T-g or T-g - 20 degrees C, while the linear monomer content has minor influence on elongation at break and strength at T-g + 20 degrees C. Finally, investigation on shape recovery behavior reveals that full recovery can be observed for each polymer when the temperature is equal to or above T-g. Also, increasing the linear monomer content results in a decrease in both shape recovery ratio (below T-g) and shape recovery speed (at T-g). These results are interpreted in terms of various crosslink densities attributed to the increasing linear monomer content.